1. Field of the Invention
The present invention relates to a packet transmission system, more particularly, to a packet transmission system by which various data signals including voice data signals can be packet-transmitted at a high efficiency with desirable transmission quality.
2. Description of the Prior Art
The packet transmission system is known as one devised for effective utilization of a circuit. The packet transmission system attains a high efficiency of circuit utilization by allowing the transmission delay time to increase to a practically permissible limit. For this reason, in a case where various digital data signals, including a voice signal, are transmitted within a given packet-communication network, if a voice signal is packetized once, there is a disadvantage in that it is impossible to connect such a packetized voice signal to a circuit switching network.
A known technique to cope with the above mentioned disadvantage of the packet transmission system is to sort data signals to be transmitted into voice signals, which require more severely restricted transmission delay time, and other data signals, which have a transmission delay time which may be relatively large. These two kinds of signals are assigned respective separately fixed time slots, so that either kind of signal may be transmitted, so as to meet the required transmission delay time characteristic within the assigned time slot. However, the number of voice signal calls decreases at night, resulting in a lowering of the rate of utilization of the channel assigned to the data signals which have a restricted transmission delay time. Therefore, the above-mentioned known technique causes the rate of circuit occupation of the whole system to decrease, and fails to achieve effective utilization of the packet transmission system, thereby making the adoption of the packet transmission system impractical.